Several economists and builders attribute the differing trajectories to the price gap between new and existing homes. While new homes almost always are more expensive, on average, than their older brethren, that gap widened since the recession.

Last month, the median new-home price of $269,800 exceeded the median existing price by 21%. Compare that to July 2008, when the gap was 12.8%. In July 2007, it was narrower still at 7.8%.

Many factors caused the gap to widen. In the existing-home market, resales of foreclosed homes at distressed prices pulled down median prices. In the new-home market, the sidelining of many first-time buyers since the recession led builders to focus onbuilding larger, more expensive homes to cater to the better-heeled, move-up buyers who still are buying.